1. Field of the Invention
The present invention relates to an improvement in a power supply device used as a power supply for driving a common driver of a line head having, e.g., an array of a large number of electroluminescence elements.
2. Description of the Related Art
A printer called an electroluminescence (to be abbreviated to as EL hereinafter) printer performs information recording on a photosensitive drum using a line head having an array of a large number of EL elements. More specifically, after the surface of a photosensitive drum whose surface is formed of a photoconductive material is uniformly changed, the surface is exposed with light emitted from the EL elements, thereby recording image information in the form of an electrostatic latent image. The electrostatic latent image is developed with a toner to form a toner image. The toner image is transferred to a paper sheet. In this manner, a printing operation is performed.
Each EL element used in such an EL printer comprises a channel electrode and a common electrode. The channel electrode is applied with a rectangular wave voltage having a voltage amplitude of +28 V, and the common electrode is applied with an AC voltage pulse which is periodically changed from, for example, +260 V.fwdarw.+15 V.fwdarw.-230 V.fwdarw.+15 V.fwdarw.+260 V, and has relatively high voltage values, thereby performing a light-emitting operation.
The AC voltage applied to the common electrode is generated by a common driver. The common driver is externally applied with voltages of +260 V, +15 V, and -230 V.
In this power supply device, however, relatively high voltages of 260 V and -230 V cannot be stopped unless external power supply is cut off. For this reason, when, for example, a paper jam occurs in a printing operation, the high voltages alone cannot be selectively stopped while the power supply is kept ON.
For example, when a paper jam occurs, a housing is opened, and the jamming paper is removed. In this case, since a high voltage generator is dangerous, the high voltages (+260 V, -230 V) must be stopped. In this case, in the conventional device, since the external power supply itself is cut off, if a printer employs a thermal fixing device, the fixing device is undesirably cooled.